You need information to be inherent to the signal in order to receive information from it. Either you need a big coherent wave that comes from an unknown direction (so that you can detect alterations in the received wavefront) or you need random noise coming from a known location (so you can detect the direction of increased noise).

Each information (i.e. non-randomness) factor adds disambiguity to the resulting detected signal. A signal of known origin and coherent timing gives you the best bet of detection the direction and range to another object.

What comes back from your coherent active sonar is already fuzzy. Any fuzziness in the input to that process increases fuzziness in the output. Eventually the fuzziness is high enough you're getting no useful information.